The invention relates to a method for determination of the layer thickness of a TBC coating on at least one rotor blade of a continuous flow machine. The invention also relates to a method for determination of the layer thickness of a TBC coating on at least one stator blade of a continuous flow machine. The invention furthermore relates to a corresponding TBC layer thickness measurement apparatus for carrying out the methods, as well as use of the method and of the TBC layer thickness measurement apparatus.
Continuous flow machines, such as steam or gas turbines, are used as thermal power machines in engineering, in order to convert energy stored in a gas flow to mechanical energy, in particular to a rotary movement.
In order to achieve as high an overall energy utilization efficiency as possible, particularly in gas turbines, the gas inlet temperatures from the combustion chamber into the flow channel of the gas turbine are chosen to be as high as possible. By way of example, according to the related art, such gas inlet temperatures are around 1200° C.
In order that the blades which are arranged in the flow channel of the turbine withstand the thermal stress, they are provided with a surface coating, a so-called TBC coating (Thermal Barrier Coating). A blade coating such as this is, however, subject to aging in that it becomes eroded from the blade as a function of the operating life over time, so that the layer thickness decreases continuously. Without the TBC coating, the blade is subject to a very high thermal load, leading to destruction of the blade. This can result in a power reduction or, in the final analysis, damage to the turbine.
WO 2004/065918 A2 specifies a method for determination of the quality of a TBC coating on blades in a continuous flow machine, as well as an apparatus for carrying out the method. In this case, electromagnetic waves are transmitted in the area of the blades, and the component of the electromagnetic waves reflected from the blades is received again and is evaluated. During the evaluation, the intensity of the received electromagnetic waves is determined, and the surface quality of the blades is then determined from this. This method allows the existence of a coating to be verified well. It is virtually impossible to obtain detailed information about the layer thickness, particularly at room temperature, since the amplitude attenuation of the electromagnetic wave is virtually lost in the system noise.